Process for producing cement



1 of the following composition:

Patented Jan. 27, 1942 UNITED STATE s [PATENT OFFICE Ole Rolfsen, Oslo,Norway No Drawing. Application February 15, 1937, Se-.

rial No. 125,933. In. Norway- Februaryr 26,

' 3 Claims.

I In the ordinary production of cement a raw material, which in thecaseofPortland cement comprises a mixture of carbonate lime, silica anda certain amount of sesq'ui-oxides, is burnt in a rotation i'umace,'ashaft furnace or a sintering apparatus, whereby there is obtained aclinker which contains besides trisilicate of lime as its main componentalso disilicate of lime and oxides of calcium-aluminum andcalcium-aluminumiron." I

As an example of an ordinary production of cement there may be mentioneda raw material Parts (about) CaCOa 120 S102 22 R20: 8

' where R203 indicates the sesqui-oxides.

By burning this raw material in a known manner there is obtained aPortland cement with substantially the following composition:

mixed with Portland cement, or on the other handa very hard-bumtPortland cement clinker by means of a process which may be carried out.in ashorter time and with less ignition losses Per cent (about) I3CaO.SiOz

.2CaO.SiOz

3CaO.A1z03 1o-15' 4CaO.A12O:Fe2Os 6-8 A difliculty which -is met with bythe production of cement in accordance with the known methods, consistsin obtaining sufficient time for the burning as the process will in manycases develop so slowly that the time is not suiflcient as well for thedissociation of the carbon dioxide oi the lime stone as for theformation of the various clinker minerals.

In different processes it has been tried to over-' come this diiiicultyin various manners for instance in the sintering process by adding largeamounts of return materials to the mixture which is to be sintered.

In spite of this considerable ignition losses due to insuflicientformation of clinker minerals have are more or less equivalent with theproperties of blast iurnace slag and which may v granulated I usedaccordingly as slag cement after being than is the case in the ordinaryprocesses for the production of cement.

In accordance with the present production of cement is carried out intwo steps, the first step consisting in burning at a comparatively lowtemperature (up to about l200 C.) and without preliminary grinding acharge which contains only a part of the amount of lime necessary forthe cement, and which may or may not comprise the amount ofsesqui-oxides necessary for the iinal product. By the treatment of thischarge at the comparatively low temperature indicated thereis obtained aproduct containing silicatesof lime, mainly disilicate of lime.

In case the burning has taken place' without I the addition ofsequi-oxidesthe disilicate of lime isobtained in the form of an unstableproduct (-3 crystals) which by cooling is caused to crumble ordisintegrate in the form of 1 crystals. In case the raw material hascontained the usual amount of .sequieoxldes and in some cases a certainamount of MgO, there is obtained a stable product which by cooling istransferred into a form approximately equivalent to granulated blastturnace slag and which may be used as addition to Portland cement in thesame manner as blast furnace slag.

In case the treatment during the first step here indicated takes placewithout the addition of sesqui-oxides, theproduct after crumbling ismixed with further amounts of carbonate of lime and sesqui-oxides,whereupon during the second step of the process it is exposed to renewedburning, whereby ordinary Portland cement clinker is obtained.

usingthe present invention.

As examples of the carrying out of the present process may be mentioned:

(a) First,step: A raw material comprising approximately -:80 partsCaC'Oa and about 22 partsSiOz i's burnt at a temperature 01' up to-1200" C. during a period vof about 10 minutes.

-There is obtained a disilicate of lime in the form of 13 crystals whichcrumbles under transformation. into '7 crystals. This product is thenmixed with further 40 parts CaCCh and 8 parts R203, whereupon it isreburnt during the second step'of the process at a temperature ofl400-l500 C. during a period of about 10 minutes. As final product thereis obtained a very hard-burnt clinker with a minimum of ignition losses.The

total time for the two burning processes is shortinvention the er thanthe necessary time for burning an ordinary Portland cement oi the normalraw material by means of the known methods.

(b) A raw material comprising approximately 75-80 parts CaCOa, about 22parts S: and about 8 parts RgOa with or without an amount of MgO isburnt at a temperature of up to about 1200 C. during a period of about10 minutes, and is then rapidly cooled. There is obtained a partlygranulated product which is approximately equivalent to granulated blastfurnace slag and which may be used accordingly.

The present method may be utilised as well in connection with theproduction of cement in rotating or shaft furnace as in the productionof cement in accordance with the draft sintering method.

In the latter case the first step of the process may be carried out in asintering pan which is connected in the current of air behind another Tsintering pan in which the burning during the second step of the processis taking, place, the

heat transferred from the last named pan with then ground in theordinary manner.

I claim: I 1. The process 'for the production of a normal cement whichcontains 3Ca0.SiOz as the predom-' inant ingredient, comprising burningat a temperature oi! substantially 1200 C. a lime silica charge whichcontains only part of the lime necessary for the final product andwherein the CaOzSiOz ratio is not substantially above 65:35 7

whereby a product which is not a normal cement but which consistspredominantly of 2CaO.SiO2 in the form of ,8 crystals results, thencooling the said product whereby conversion to 7 crystal form withsimultaneous disintegration results, admixing the resultant product withthe additional lime required for a normal cement, grinding theadmixture, reburning the latter at a temperature of up to about1400-1500 C., and finally grinding the resultant product whereby anormal cement results.

2. The process for the production of a normal cement which contains3CaO.SiO= as the predominant ingredient, comprising burning at atemperature of substantially 1200 C. a charge containing substantiallyonly limestone and silica and comprising less calcium carbonate withrelation to the silica than the amount necessary for the formation ofthe final product, the CaOzSiO: ratio'in said charge being notsubstantially above :35, whereby a product which is not a normal cementbut which consists predominantly of 2C9.O.S1O2 in the term of 3 crystalsresults, then. cooling the said product whereby conversion to 7 crystalform with simultaneous disintegration results, admixing the resultantprodnot with the additional lime required for a normal cement, grindingthe admixture, reburning said charge being not substantially above65:35,

whereby a product which is not a normal cement but which consistspredominantly of 2Ca0.SiO2 in the iorm of ,8 crystals results, thencooling the said product whereby onversion to '7 crystal form withsimultaneous integration results, admixing the resultant product withadditional lime and sesquioxides oi aluminum and iron in the 1 amountrequired for a normal cement, grinding I the admixture, reburning thelatter at a temperature of up to about 1400-1500 C., and finallygrinding the resultant product whereby a normal cement results. I

OLE ROLFSEN.

